Positive Feedback and the Runaway Greenhouse

Two recent reports about climate change research send up red hot flares warning of positive feedbacks promoting global warming.

The first is a report by Richard Kerr in Science magazine (see Kerr 2009) of research conducted by Amy Clement and colleagues at the University of Miami in Florida. The bottom line in this study finds that warming ocean temperatures may cause low clouds to thin, allowing more sunlight to reach the ocean and cause further warming of the ocean surface. In turn, this increased warming could cause further cloud thinning allowing even more sunlight to reach and warm the ocean. This positive, or reinforcing feedback provides one of the more frightening scenarios of climate change. The runaway greenhouse effect that a positive feedback loop could trigger threatens to make the worst predictions of the IPCC look tame.

The second report, by Charles Hanley of the Associated Press (see Hanley 2009), examines the findings of a host of permafrost scientists from Canada, Russia, the United States, Germany, Britain, Norway, and Sweden. The common thread here involves permafrost melting across the far northern hemisphere in response to rising temperatures. The danger lies with the large amounts of methane locked in the, until now, permanently frozen lands of the Arctic. If those lands thaw and release this methane, it would add significantly to the already dangerous greenhouse effect from the excess carbon dioxide we have added to the atmosphere since the beginning of the industrial revolution. Methane's greenhouse gas potential, molecule for molecule, is 21 times that of carbon dioxide. The release of even a fraction of the many billions of tons of methane locked up in the Arctic would cause a degree of increased warming sure to melt even more permafrost, and yes, you guessed it, release yet more methane. That should sound familiar, as it represents one more way that a positive feedback cycle threatens to produce a runaway greenhouse effect and catastrophic global warming.

And while climate scientists have been aware of both of these positive feedback possibilities for years, these new findings suggest that the possibilities may become reality. Both reports underline the need for continuing research, but both also point to a growing risk of extremely nasty climate surprises.

Climate skeptics are quick to point out that climate predictions may exaggerate the dangers of global warming. These two reports underline the fact that climate predictions may also greatly underestimate future global warming.

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Hanley, C.J. 2009. Climate trouble may be bubbling up in far north. News and Observer, Raleigh, NC. September 3, 2009 (Associated Press).

Kerr, R.A. 2009. Clouds appear to be big, bad player in global warming. Science 325:376.